This invention relates to techniques for axially aligning radially inner and outer shell components of steam turbines, particularly useful in field applications.
In double shell type turbine construction, alignment of the inner shell to outer shell is typically accomplished by male-to-female fit components on both upper and lower separable halves of the inner and outer shell components. Thus, there are two pairs of axial alignment fits, one pair between the upper halves of the radially inner and outer turbine shell components, and a second pair between the lower halves of the inner and outer turbine shell components. Often, these fits are strictly for axial positioning of the inner shell relative to the outer shell. During replacement of the inner shell for conversion, modernization, or uprate, the new inner shell is initially machined with additional material on the axial fits to allow for field machining to obtain the proper axial alignment. Benchmarking allows the correct axial position to be determined; however, the necessary equipment to machine the inner shell fits is not available in the field. This requires transport of the inner shell to a local machining facility, setup, machining and transport back to the power generation site, resulting in costly delays in the installation cycle.
This invention relates to a new design for locally machinable keys for each female fit component that facilitates axial alignment of the inner and outer turbine shell components. Once the correct axial position of the inner to outer shell is determined, the keys may be machined in the field to the correct thickness that will insure correct axial alignment. The keys are made to be easily assembled and disassembled for turbine maintenance, and may be reused.
In the exemplary embodiment, a pair of xe2x80x9cLxe2x80x9d shaped keys are dimensionally sized according to the axial alignment fit dimensions. Each axial alignment fit includes a female component on the inner shell with a pair of adjacent, horizontally outwardly extending projections or flanges forming a slot or channel, and a male component on the outer shell, with a single horizontally inwardly extending projection or flange adapted to fit in the slot or channel of the female component. Two keys are placed in each female component of the fit, (a left and a right handed key, one on each of the female fit component flanges), and bolts or cap screws are used to retain each key on the fit. The position of the screws prevents distortion of the keys in the radial direction during thermal transients. Two dowels are also included for shear strength in the vertical direction during disassembly, and for further insuring axial alignment of the inner and outer shells after the final positioning. The faces of the keys are engaged by the male component on the outer shell are surfaced with stellite to provide for ease of disassembly. The weight of each key is approximately 40 pounds, which provides for ease of installation by a single field technician and alleviates the need for complex lifting equipment.
Accordingly, in its broader aspects, the invention relates to a turbine shell assembly comprising radially inner and outer shell components; axial alignment fits on said inner and outer shell components, each alignment fit comprising a male component on one of said inner and outer shell components and a female component on the other of said inner and outer shell components, the female component comprising a pair of tabs forming a U-shaped channel with opposed faces, and the male component comprising a projection received within said U-shaped channel; and a pair of axial alignment keys, each key having a mounting flange for securement along an outer edge of a respective one of said pair of tabs and an alignment flange engaged along a respective one of said opposed faces.
In another aspect, the invention relates to an alignment key for a female fit component on a turbine shell component, the key comprising a mounting flange and an alignment flange, the mounting flange having a plurality of fastener holes therein that are oversized relative to fasteners adapted for use therewith; the alignment flange extending perpendicularly relative to said mounting flange, the alignment flange having a hardened face thereon.
In still another aspect, a method of axially aligning inner and outer turbine shell components each having upper and lower halves comprising a) providing a first pair of axial alignment fits between the upper halves of the radially inner and outer turbine shell components, and a second pair of axial fit components between the lower halves of the radially inner and outer turbine shell components, each axial alignment fit comprising a male fit component and a female fit component, the female fit component comprising a pair of tabs forming a U-shaped channel with opposed faces, and the male fit component comprising a projection adapted to be received within the U-shaped channel; b) axially aligning the radially inner and outer shell components; c) providing a pair of alignment keys for each axial alignment fit, each key having a mounting flange for securement along a respective outer edge of a respective one of the tabs, and an alignment flange engageable along a respective one of the opposed faces; d) determining the precise location of the male fit component within the U-shaped channel; e) machining one or both of each the pair of alignment keys along back faces of the alignment flanges to enable the precise location; f) fastening the keys to the outer edges with a plurality of fasteners; g) drilling dowel holes in the mounting flange and into the radial edge; and h) inserting dowel pins within the dowel holes.